[IRCA] ? 4 ULR/DSP experts: -25kHz wide splatter in ±1k BW, strong signal pumping?

[Stephen Airy <pianoplayer88key@xxxxxxxxx>]

Hello, ULR / Tecsun DSP radio experts (N7EKX, VA3SW, KE7MAV, etc)... :)


I've noticed that one of my medium-strength locals, 910 KECR (about 67 dBµ on the PL-398mp - an uncleanable smudge seems to make it look like 87 dBµ) seems to have quite a wide splash, even in the ±1kHz bandwidth mode.  The two videos below are recorded with the larger-than-ULR PL-398mp, but the ULR-sized PL-606 (broken LCD display) and PL-380 (broken tuning knob, some nearly-impossible-to-press buttons) also do the same thing.


https://www.youtube.com/watch?v=o_kQ6gVuCSo

As you can probably tell, the splatter is easily noticeable down in the low 890s.  (The other radio is tuned to 910 to attempt to confirm the source of the modulation splats.)  Near the end of the video during the talking segment, I even hear blips of modulation splats down around 885 or 886 kHz.  Any idea why this would be happening?  It makes pulling in daytime DX targets on 900 and 920 impossible, and 890 and 930 difficult, unless the station is off the air.  ("Thankfully" - in quotes because I actually like some of their programming - KECR seems to be the most likely to be off the air when something goes "wrong".)


The nearest target on 900 would be 500-watt KALI West Covina.  I'm in a deep notch, though, and have been unable to confirm hearing them even when KECR was off the air one early afternoon a couple Februarys ago.  On 920, KPSI Palm Springs or XESDA Ensenada should both be much easier targets, if it weren't for KECR, but they're basically the same or reciprocal directions, so I can't null KECR and bring in the others.  (I'm just barely outside XESDA's supposed 0.15mV/m contour per Radio-Locator, whom I suspect greatly underestimates Mexico's ground conductivity.  See their daytime map of omni-directional KBLU-560 for example.)

You may have noticed RSSI dBµ numbers below 15 in the 880s, only rising as you were near 910.  I've found a trick on the PL-398mp that enables this.  A demonstration (in a bandscan video - warning, entire vid is 27+ min) is found in https://www.youtube.com/watch?v=BJl5lebq4jY near the beginning.  You turn the radio on, go to SW, hold the VF button until it starts scanning, then quickly rotate the tuning down.  The background noise will be *much* louder, and the radio will be set in ±2kHz BW.  Using this technique, I am able to take Radio Disney's barely-audible 45/00 signal on 1110-KDIS (desensing due to 75/25 1130-KSDO and 80/25 1170-KCBQ) and turn it into a listenable 22/~16 signal.  I've heard that some models of the PL-310 can do this, and am wondering if any other DSP radios can?  I'm unable to do it on my PL-380 or PL-606, I suspect due to various other things being wrong with it.



I also noticed that KECR, especially when in the ±6kHz BW setting, has severe audio pumping.  I thought this was something that normally only happened with very weak stations?  Yet the KECR video above has it around the middle, with its mid-strength local-grade signal.

https://www.youtube.com/watch?v=L0C_VIJpyZ0

This video has it too - even on a moderately strong signal (~94-95 dBµ in my front yard - yes, with a little off-camera enhancement) on the PL-398mp.  I notice that the S/N display shows 25dB during quiet spots, and often 00 dB or so during loud passages.  This seems opposite of what I would expect.  I also sometimes notice the audio pumping on 620-XESS, 1030-XESDD, 1090-XEPRS and 1700-XEPE, which range in the low 40s to mid 50s dBµ signal strength and are essentially local reception.

Any ideas what could be the cause?


73, Stephen

P.S. what barefoot ULR would N7EKX use to get reception of his nearby Family Radio affiliate, 1460-KARR, comparable to what's in this video, while in his backyard? ;) https://www.youtube.com/watch?v=tjoL9oqEVZM
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